The formation of a buried contact through a relatively thin layer of silicon dioxide, which functions as a gate oxide for a field effect transistor (FET), for example, on a surface of a silicon substrate has previously been accomplished through depositing a layer of photoresist on the relatively thin layer of silicon dioxide on the substrate and then forming an opening in the layer of photoresist by a conventional photolithographic technique. This enables the photoresist layer to function as a mask for forming the opening in the relatively thin layer of silicon dioxide through which an electrical contact is to be made to the silicon substrate. After the opening has been formed in the layer of photoresist, the relatively thin layer of silicon dioxide has been etched by a suitable etchant such as a buffered hydrofluoric acid solution, for example.
After etching of the relatively thin layer of silicon dioxide, the layer of photoresist has been removed. During removal of the layer of photoresist, a very thin layer of silicon dioxide has been formed on the exposed surface of the silicon substrate. This very thin layer varies in thickness from 15 A to 30 A depending on the procedure employed to remove the photoresist. If a wet etch is used to remove the photoresist through employing sulfuric acid (H.sub.2 SO.sub.4) as the etchant, for example, the oxygen in the etchant reacts with the silicon substrate to form a layer of silicon dioxide having a thickness of approximately 15 A to 25 A. When a dry etch is utilized in which oxygen plasma is employed as the etchant, for example, the oxygen reacts with the exposed surface of the silicon substrate to form a layer of silicon dioxide having a thickness of approximately 25 A to 30 A.
This very thin layer of silicon dioxide can cause an increase in the resistance of the contact if it is not removed because of its electrical insulation property. Thus, this increase in the resistance would prevent the contact from functioning satisfactorily so that the end product is defective.
If the very thin layer of silicon dioxide is removed by a buffered hydrofluoric acid solution, for example, to avoid the increase in resistance of the contact, the relatively thin layer of silicon dioxide through which the contact opening has been formed is etched to a degree. This can degrade the layer of silicon dioxide sufficiently through reducing its thickness so that it may no longer function satisfactorily as a gate oxide layer, for example, in a FET.
The relatively thin layer of silicon dioxide cannot have its thickness increased to compensate for the removal of silicon dioxide therefrom at the time that the very thin layer of silicon dioxide is removed by a buffered hydrofluoric acid solution. This is because the amount of reduction of thickness of a layer of silicon dioxide cannot be controlled to the degree necessary to obtain the desired final thickness of the relatively thin layer of silicon dioxide so that it may function as a gate oxide, for example. Furthermore, this type of removal of silicon dioxide can produce defects therein. Accordingly, it is not possible to make the relatively thin layer of silicon dioxide, which is to function as a gate oxide, for example, slightly thicker to compensate for removal of a portion thereof when the very thin layer of silicon dioxide is removed from the substrate surface.